1998 Honda accord ex sedan, engine shuts down at random times while driving

So ever since march of 2017 I've been driving my grandpas Honda accord
which he gave me. before 2017 it was sitting in my grandpas garage
untouched for 3 years but about a week after i started driving it, the engine
shut off while i was driving the car to work. And ever since I got the car in
march up until now, it has shut off 4 times while driving. I don't know what the
issue is and i brought it into a mechanic to get them to fix it but they could
not find the problem and at this point i have no confidence when driving the
car because I am afraid it will shut off at any time so does anyone have an
idea of what it could be?